Glossary

Anoxic Ecosystems

An aquatic environment that is devoid of oxygen.


Baseflow

The depth of water in a stream when the channel is fed solely by groundwater.


Carbon Sequestration

The act of growing plant material and accumulating biomass to intentionally remove carbon dioxide, a green house gas, from the atmosphere. Carbon sequestration is often done to mitigate global climate change caused by atmospheric carbon dioxide.


Conveyance

The transportation of water away from an area to avoid flooding.


Design Storm

A rain event that is used as a worst probable scenario when calculating what volume and flow rate of water needs to be stored or treated.


Evapotranspiration

A combination of the effects of water evaporation and plant transpiration.


Exfilration

The process of subsurface goundwater moving away from the point of infiltration and dispersing through the rest of the soil.


Filtration

The reduction in concentration of chemical and physical pollutants in water caused by passing the water through screens. In the treatment of stormwater quality the screens used are usually the void spaces between sand particles, but can also be biological filters.


Geotextiles

Porous fabrics that have been designed to allow only soil particles of a certain size to pass through. They are used to filter pollutants from water, and to provide structural support.


Hydraulic Conductivity

A measure of the ability of water to pass through soil.


Impervious Surface

A type of land cover that does not allow for water to pass through it, such as rooftops and roadways. Impervious surfaces cause rain water to quickly shed off.


Infiltration

The process by which water travels from the ground surface into the soil underneath.


Isopluvial

A line drawn on a map that connects points that have the same pluvial index, such as precipitation. Similar to how a contour line connects points with the same elevation.


Landscape Island

A garden, usually enclosed by a curb, that is surround on all sides by either a parking lot or a roadway.


Longitudinal Slope

The measure of steepness of a channel in the direction of water flow.


Low Impact Development

Choosing to use the infrastructure alternative that has the smallest effect on the environment, but still performs its desired function.


Permeability

A measure of the ability of soil to transmit water.


Porosity

The fraction of volume taken up by air pockets in a soil layer.


Thermal Stratification

When the upper strata of a lake are heated by the sun's rays, but the lower strata are not causing a difference in water density and preventing the water exchanging between strata.


Transpiration

The evaporation of water from plants.


Underdrain

A perforated PVC pipe that runs below an infiltration system. The piping collects treated water, and moves it to a larger underground storm sewer.


Void Space

The unoccupied area between soil particles usually filled by air, unless the soil is saturated.


Water Quality

The physical, biological, and chemical constituents found in a sample of water. The following four parameters describe water quality.


Biological Oxygen Demand (BOD)

The amount of oxygen required by microbial organisms to digest the carbon-based material in a water sample at a given temperature over a given period of time.


Hydrocarbons

A chemical that consists only of hydrogen and carbon. Hydrocarbons are often left on parking and road surfaces by the petroleum products used to grease vehicles.


Organic Nutrients

Chemicals, usualy nitrogen and phosphorous based, that reside on the land surface as a result of fertilizer runoff.


Total Suspended Solids (TSS)

An aggregate measure of water quality that describes the amount of solids, ususally soil particles, found in a water sample.


Water Quantity

Refers to the amount of rain water that either pools on or sheds off of the land surface. Quantity is a function of rainfall intensity and duration. The following two parameters describe water quantity.


Peak Runoff Rates

The discharge associated with the peak runoff volume, or the volume over time.


Peak Runoff Volumes

The depth of rainwater that falls on an area that has to be treated or managed by stormwater infrastructure.